The present invention disclosed herein relates to a target for generating positive ions, a method of fabricating the same, and a treatment apparatus using the target, and more particularly, to a target for generating positive ions using surface plasmon resonance, a method of fabricating the same, and an ion beam treatment apparatus using the target.
Radiation treatment methods include X-ray, electron beam, and ion beam treatment methods. Since an X-ray treatment method is the least expensive method that may be realized by using the simplest apparatus, the X-ray treatment method is currently the most commonly used among the radiation treatment methods. That a tumor may be treated when electrons are accelerated by an accelerator to be injected into the tumor is proved in the 1950s. However, an electron beam treatment has been regularly established as a method of radiation treatment after the miniaturization of an electron accelerator was realized in the 1980s. Meanwhile, the X-ray treatment or the electron beam treatment may destruct deoxyribonucleic acid (DNA) of cancer cells by disconnecting hydrogen bonds in the cancer cells, but may be accompanied by a side effect that seriously damages healthy cells located in a progressing path. A technique, such as Intensity-Modulated Radiation Therapy (IMRT) or Tomo Therapy and Cyber Knife, has been developed as a method of reducing radiation exposure with respect to normal cells. However, the above methods may not completely address the foregoing side effect.
An ion beam treatment method has received attention as a treatment measure capable of reducing the side effect generated in the X-ray treatment or the electron beam treatment. In order for an ion beam to transmit a material, the ion beam must have a fast speed by being accelerated as in the case of electrons. Although the speed of an ion beam may be gradually reduced when the ion beam transmits a certain material, the ion beam may experience the highest energy loss of ionizing radiation just before the ion beam stops. Such a phenomenon is referred to as “Bragg Peak”, named after William Henry Bragg who discovered the phenomenon in 1903. Therefore, with respect to the ion beam treatment method, a selective as well as localized treatment with respect to malignant tumors may be possible when the speed of ions is accurately controlled. In the case where a tumor is located deep inside the body, protons or ions having relatively high energy must be accelerated from the outside of the body. There is a laser driven ion acceleration method among methods of accelerating such protons or ions. When a thin film is irradiated with a high-power laser beam, ions or protons in the thin film may escape from the thin film while having acceleration energy by a target normal sheath acceleration (TNSA) model or a radiation pressure acceleration (RPA) model. A general principle of the ion beam treatment may be described by that the escaped ions may transmit the body of a patient as deep as the energy of each ion and may stop at a predetermined depth at which a tumor is located, and tumor cells are necrotized while a large amount of free oxygen radicals is generated in the stopped region.
There are broadly two properties that ions must have in the ion beam treatment method using the laser driven ion acceleration method. Ions must be in a state of high energy in order to be injected deep into the body and most of the ions must have the same energy. Protons having an energy of about 250 MeV may transmit about 20 cm of the body. With respect to an ocular cancer treatment, high-energy ions having an energy of about 70 MeV are required and with respect to the treatment of cancer located deep inside the body, high-energy ions having an energy of about 200 MeV or more are required.
Also, energies of most of protons or ions driven by a femtosecond laser must be uniform. The reason for this is that when the energies are not uniform, ions may not be focused only to the position of a tumor, and thus, there may be possibility that normal tissues may be exposed by the ions.
In order to satisfy the above two properties, a thickness of a target as a source of ions must be very small. Therefore, the target must be an ultra thin film.
A laser for accelerating such ions must have a relatively high energy ranging from about 1019 W/cm2 to about 1021 W/cm2. This means a relatively large laser system and thus, a large budget may be required.